Design of iodinated radioligands for SPECT imaging of central human 5-HT₄R using a ligand lipophilicity efficiency...

A series of iodinated ligands for the SPECT imaging of 5-HT₄ receptors was designed starting from the previously reported hit MR-26132. We focused on the modulation of the piperidine-containing lateral chain by introducing hydrophilic groups in order to decrease the liphophilicity of the new ligands. All the synthesized compounds were tested for their binding affinities on 5-HT₄Rs and based on the Ligand Lipophilicity Efficiency approach, compound 13 was further selected for radioiodination with iodine-125 and imaging experiments. Compound 13 showed its ability to displace the specific signal of the reference compound [¹²⁵I]SB-207710 but no significant detection of [¹²⁵I]13 was observed in vivo in SPECT experiments.